This invention relates generally to a device for previewing the field of view of an optical lens for use in still, motion picture or video photography. In such applications it is frequently necessary to be able to estimate the focal length of the lens required from a number of different camera positions. This estimation in many instances must be made without the use of the camera or the lens itself, since these are usually unavailable at the time of estimation. In these situations, a device other than the lenses themselves must be used to be able to estimate the types, sizes and number of lenses required.
Devices for previewing the focal length of lenses have been known in the art. However, such devices generally utilize optical elements to preview the field of view of the lens. Clearly, devices using optical elements are in themselves, expensive, bulky and relatively difficult to use. The present invention is directed to overcoming these difficulties.
Generally speaking, in accordance with the invention, a device for previewing the field of view of optical lenses is provided. The device utilizes an adjustable aperture corresponding in dimension to the aspect ratio of the image formed by the lens. A spacing member spaces the user's eye away from the aperture to simulate the field of view of the lens as seen through the field of view of the aperture. As the aperture is adjusted, the device reads out the proper focal length of the lens to be used with the various film and video formats.
Accordingly, it is an object of this invention to provide an improved device for previewing the field of view of optical lenses.
It is another object of this invention to provide a previewing device that does not require the use of optical elements.
It is another object of this invention to provide a previewing device that is compact and easy to use.
It is another object of this invention to provide a previewing device that is relatively inexpensive to manufacture and use.
Still other objects of this invention will become apparent upon a reading of the detailed specification to follow.